Method of operating a hydraulic system for a loader machine

ABSTRACT

A method of operating a hydraulic system of a loader arm carrying a working implement, the system having a ride improvement system and a selection valve connected to first and second chambers of a ram which operates the loader arm. A check valve assembly is provided, with the check valve assembly being responsive to pressure changes in the second chamber. The check valve assembly, when closed, prevents fluid from passing between the first chamber to the selection valve. Means are provided communicating the fluid pressure in the second chamber to the check valve, with the means responsive to pressure changes in the second chamber to open the check valve. The selection valve is operable to raise the loader arm with the system arranged to permit passage of fluid between the first chamber and the accumulator while permitting fluid to pass from the second chamber to a low pressure region.

BACKGROUND OF THE INVENTION

This invention relates to a method of operating a hydraulic system for aloading machine, such as a wheeled loader having a loader arm assemblywhich carries a working implement and in which the loader arm assemblyis connected to the body and which is movable between raised and loweredpositions by means of a hydraulic ram.

It is known to improve the ride of a wheeled loader by connecting anhydraulic accumulator into the hydraulic hose which feeds hydraulicfluid into said ram means to raise the loader arm assembly. As a resultwhen the wheeled loader is travelling across a site, or when travellingalong a road, the loader arm assembly is suspended in spring manner bythe accumulator and so the wheeled loader is able to travel with lesspitch and bounce than would otherwise have been the case.

However, such a ride improvement system has not been provided hithertoin a loader vehicle including a loader arm assembly connected at, oradjacent to, the rear end of the assembly to the body at, or adjacentto, the rear end of the body so that the loader arm assembly extendsforwardly whereby, in a lowered position of the arm assembly, theworking implement is disposed in front of the body, where such a vehicleis provided with a hose burst check valve.

SUMMARY

According to at least one disclosed example of the present invention, weprovide a method of operating a hydraulic system of a loader machine,the loader machine having a loader arm assembly connected to a body sothat in a lowered position of the loader arm assembly, a workingimplement carried at an outer end of the loader arm assembly is disposedin front of the body, and which loader arm assembly is movable betweenraised and lowered positions by means of a hydraulic ram of thehydraulic system, the hydraulic system further including a rideimprovement system including a hydraulic accumulator which is connectedto the hydraulic ram, and a selection valve connected to each of a firstand second chamber of the hydraulic ram, and a check valve assemblyconnected between the first chamber and the selection valve such thatthe check valve, when in a closed condition, prevents fluid underpressure passing from the first chamber to the selection valve, and thecheck valve assembly having hydraulic fluid responsive means responsiveto hydraulic fluid pressure in the second chamber to move the checkvalve assembly to an open condition, and there being means to connectthe hydraulic fluid pressure in the second chamber to the check valveassembly, the method including operating the selection valve to raisethe loader arm assembly by feeding fluid under pressure to one chamberof the ram and to receive fluid at a lower pressure from the secondchamber of the ram, or to lower the loader arm assembly by feeding fluidunder pressure to the second chamber of the ram and to receive fluid ata lower pressure from the first chamber of the ram, and wherein themethod includes operating the selection valve to raise or lower theloader arm assembly, and when the selection valve means is operated toraise the loader arm assembly, permitting the passage of hydraulic fluidbetween the first chamber of the hydraulic ram and the accumulator, andwhilst permitting the passage of hydraulic fluid from the second chamberto a low pressure region.

Desirably, when the selection valve is operated to lower the loader armassembly, the passage of hydraulic fluid from the second chamber to thelow pressure region is prevented, and thus sufficient hydraulic pressurewill be provided to the hydraulic pressure sensing means to open thecheck valve assembly and to permit fluid to pass from the first chamberof the ram, back to the selection valve.

If desired, the method may include moving a first control valve which isconnected between the first chamber of the hydraulic ram and thehydraulic accumulator, between a first position in which the passage ofhydraulic fluid between the first chamber of the hydraulic ram and theaccumulator is permitted and a second position in which passage ofhydraulic fluid to the accumulator is prevented. However in anotherarrangement, such a first control valve need not be provided, so thatthe ride improvement system is potentially permanently in an activecondition.

The method includes moving a control valve which is connected betweenthe second chamber and the low pressure region between a first positionin which passage of hydraulic fluid therethrough to the low pressureregion is permitted, in which condition the loader arm assembly may beraised, and a second position in which the flow of hydraulic fluid tothe low pressure region is prevented, so that the loader arm assemblymay be lowered.

Although the step of moving the control valve which is connected betweenthe second chamber and the low pressure region between its first andsecond positions may be carried out purely manually, in a preferredarrangement the selection valve is provided with a switch to sense whenthe selection valve is operated to lower the loader arm assembly, andwherein the method includes sensing operation of the selection valve tolower the loader arm assembly, and moving at least the second controlvalve to the second position in response. Thus, in accordance with thedisclosed example, the method step of moving the control valve to permitlowering of the loader arm assembly may be achieved automatically.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying drawings wherein:

FIG. 1 is a side view of a vehicle according to the invention,

FIG. 2 is a diagrammatic circuit diagram showing the flow of hydraulic:fluid and valve positions in normal operation of the vehicle duringlifting of the arm,

FIG. 3 is a view similar to that of FIG. 2 but showing normal operationduring lowering of the arm,

FIG. 4 is a view similar to that of FIG. 2 but showing a travel positionof the vehicle with the ride improvement means engaged,

FIG. 5 is a view similar to that of FIG. 4 but showing a boom liftposition and ride improvement means engaged.

FIG. 6 is a view similar to that of FIG. 4 but showing flow of fluid ina boom lower position with the ride improvement means engaged;

FIG. 7 is a diagrammatic circuit diagram of a second embodiment of theinvention.

DETAILED DESCRIPTION

Referring to the drawings, a wheeled loader vehicle includes a body 10supported, in conventional manner, on two pairs of front and rear wheels11, 12 each of which is steerable and each of which is driven by asuitable transmission and differential means from an engine which may bedisposed as desired on the vehicle. The body 10 has a rear end 13 and afront end 14. A loader arm assembly 16, at a position adjacent its rearend, is pivotally mounted to the body 10 adjacent the rear end 13 of thebody, about an axis 15. The loader arm assembly 16 in the presentexample, is a two part boom having an outer part 16 a, within which istelescoped an inner part 16 b and which parts are slidable relative toeach other by hydraulic ram means so as to provide an extendible loaderarm assembly. If desired the vehicle may have a two or more part boom oran un-extendible single part boom.

At the front end of the boom assembly 16 is a downwardly extending nosepart 17 by which a working implement 18 is releasably carried inconventional manner. If desired, the working implement 18 may be a pairof lifting tines as shown or may be a bucket or any other suitableworking implement.

The loader arm assembly may be connected to the body at or adjacent therear thereof, by any suitable pivot means disposed at or adjacent therear of the loader arm assembly.

The loader arm assembly 16 is pivotable about the axis 15 between raisedand lowered positions. In the lowered position working implement 18 isdisposed in front of the vehicle front end 14. The loader arm assembly16 is movable between said raised and lowered positions by a ramassembly 20, which in the present example includes a single ram. The ramassembly 20, in conventional manner, includes a cylinder part 21 and apiston rod 22. The piston rod 22 is connected at one end to a bracket 23depending downwardly from the underside of the part 16 a of the loweredarm assembly by means of a pivot pin 24 a whilst the cylinder 21 isconnected, at its lower end, by a pivot pin 24 b to a part of the body10. Obviously extension and retraction of the piston rod 22 from thecylinder 21 causes pivotal raising and lowering of the arm assembly 16.

Within the cylinder 21 is a first chamber 25, on one side of the piston27, which is of cylindrical configuration and a second chamber 26 on theopposite side of the piston 27, see FIGS. 2 to 5, to the first chamber25 and which is of annular configuration in cross section. Mounted onthe cylinder 21 is a conventional accumulator means 30 made of, in thepresent example, steel and connected by a pipe 31 to a first controlvalve 32. A second control valve 33 is connected by a line 34 includingflexible hoses and/or rigid pipes to an hydraulic reservoir or other lowpressure area 35.

Each control valve 32, 33 is an electrically operated solenoid valve andwhich is movable between a first or “at rest” position in which passageof fluid is prevented in one direction of the valve 32 and in bothdirections in the valve 33 and a second position in which passage offluid is permitted. Both control valves 32, 33 are normally springbiased by a spring means 36 to the position in which flow of fluid isprevented as illustrated in FIG. 2 and FIG. 3.

A line 38, including a rigid pipe 38 a and a flexible line 38 b,connects the first chamber 25 of the ram 20 to a first port 40 a of aselection valve 40 via a hose burst check valve 39. The first controlvalve 32 is connected by a line 37, including a rigid pipe, to the line38 between ram chamber 25 and the hose burst check valve 39. The hoseburst check valve 39 is a pilot valve that is normally maintained closedin the direction to prevent flow of fluid under pressure from thechamber 25 to the valve 40 but it may be opened by supply of pilotpressure on line 41, including a rigid pipe, from a line 42, including arigid pipe 42 a and flexible hoses 42 b which extends between a secondport 40 b of the selection valve 40 and the chamber 26 of the ram 20.The line 42 is connected by a line 43 to the second control valve 33.

In use, as best shown in FIG. 2, during normal operation, when it isdesired to lift the arm, fluid under pressure is fed from the first port40 a of the selection valve 40 along the line 38 through the one-waycheck valve within the hose burst check valve 39. As boom suspension hasnot been selected there is no electrical supply to valves 32 and 33 andthey remain in the normally closed position. As the telescopic boom 16is raised, by the supply of fluid to the chamber 25, fluid under lowerpressure is fed from the chamber 26 along line 42 into a port 40 b ofthe selection valve 40. The valve 33, of course, being, like the valve32, maintained in the position shown in FIG. 2 to prevent flow of fluidtherethrough by virtue of no electrical supply being supplied to thesolenoid thereof.

Referring now to FIG. 3, when it is desired to lower the loader armassembly the valve 40 is actuated to feed fluid under pressure throughport 40 b along line 42 into the chamber 26 and thus fluid under lowerpressure is fed from chamber 25 along line 38 through hose burst checkvalve 39 which is maintained in an open position by virtue of supply ofpilot pressure on line 41 which extends from line 42.

Referring now to FIG. 4, when it is desired to operate the rideimprovement means i.e. boom suspension means the system is activated byoperation of a suitable electric control so that electrical supply isprovided to the valves 32, 33 to move them from the positions shownFIGS. 2 and 3 to the positions shown in FIGS. 4 to 6 in which passage ofhydraulic fluid is permitted.

In this position fluid can flow both to the accumulator 30 and also tothe reservoir 35 in accordance with the external forces imposed on thepiston 27 to displace fluid to or from chambers 25, 26. Such a conditionis shown in FIG. 4. As a result the loader arm is supported by theaction of the accumulator on the hydraulic fluid and it is, in effect,sprung.

Referring now to FIG. 5, when it is desired to raise the loader armassembly whilst the ride improvement means is engaged, the valve 40 isactuated to feed fluid from port 40 a under pressure along line 38 intothe chamber 25 whilst fluid from the chamber 26 passes along the line 42back to the valve 40. At the same time the suspension of the armassembly is suspended by the accumulator 30 as described hereinbefore inconnection with the FIG. 4.

Referring now to FIG. 6, when it is desired to lower the boom whilst theride improvement means is engaged, the actuation of the valve 40 toraise pressure at port 40 b, by virtue of switch 44, has the effect ofcollapsing the electrical signal to valve 33 which becomes closed and soallows pressure to be raised in line 42 which feeds fluid under pressureto chamber 26, whilst fluid in chamber 25 is fed via line 38 through thehose burst check valve 39 to the port 40 a of the valve 40. The hoseburst check valve 39 is maintained open by pilot pressure fluid on line41 which extends from line 42.

Whilst in this example the accumulator 30, valves 32, 33 and check valve39 are all disposed on the cylinder 21, if desired one or more of thesecomponents may be positioned as desired and made of material as desiredwhere permitted by local regulations.

Referring now to FIG. 7 an alternative embodiment is illustrated.Similar parts to those shown in FIGS. 1 to 6 are indicated by the samereference numerals.

In this example, the first control valve indicated at 32 in thehydraulic system of the previous figures, is removed, and theaccumulator 30 is connected by the rigid pipe 37 to the line 38 at apoint between the hose burst check valve assembly 39 (or check valveassembly 39) and the ram assembly 20.

The loader vehicle operates similarly to the loader vehicle describedwith reference to the previous figures, to provide both ride improvementand hose burst protection, by the provision of the host burst protectionor check valve assembly 39.

However, it will be appreciated that without the presence of the firstcontrol valve 32 which is moveable as described above to a secondposition to prevent the flow of hydraulic fluid to the accumulator 30,the ride improvement system would be permanently “on” or active.

In a first active state, when the second control valve 33 is in the “atrest” or first position shown in FIG. 7, it will be appreciated that itis possible to raise the loader arm assembly 16 by operating theselection valve 40, to develop pressure in the lines 38 b and 38connected to the first chamber 25 of the ram assembly 20 with fluidexpelled from second chamber 26 passing along line 42 back to theselection valve 40, the hose burst protection valve assembly 39maintaining the condition shown in FIG. 7 to provide protection in theevent of a hose burst in the line between the hose burst protectionvalve 39 and the selection valve 40.

Moreover in the first active state, the loader arm assembly 16 may belowered by operating the selection valve 40, to develop pressure in theline 42 to and in the second chamber 26 of the ram assembly 20. Pressuremay be thus developed in the line 42 and second chamber 26 because thesecond control valve 33 is in its first position i.e. closed to preventfluid passing from the line 42 to the low pressure region 35. Thus apilot pressure is transmitted, along line 41, to the hose burstprotection or check valve assembly 39 which thus moves to the conditionindicated in FIG. 3, so that fluid expelled from the first chamber 25may pass through the hose burst protection or check valve assembly 39back to and through the selection valve 40.

In a second active state, whilst the line 38 between the hose burstprotection or check valve assembly 39 and the ram assembly 20 isconnected to the accumulator 30 by virtue of the absence of the firstcontrol valve 32, the second control valve 33 is moved to secondposition shown in FIG. 4 when fluid flow from the line 42 between thesecond chamber 25 of the ram assembly 40 and the selection valve 40,through the second control valve 33 to the low pressure region 35, ispermitted. In this state, although ride improvement is provided as theaccumulator 30 is still connected to the line 38 between the host burstprotection or check valve assembly 39, and the first chamber 25 of theram assembly 20, and the loader arm may be lifted by applying pressureto lines 38 b/38. However, fluid expelled from the second chamber 26 ofthe ram assembly 20 may pass to the low pressure region 35 through thesecond control valve 33.

It will be appreciated that the primary role of the second control valve33 when in its first “at rest” position is to prevent the flow ofpressurised fluid from the line 42 connected to the second chamber 26 ofthe ram assembly 20, to the low pressure region 35, although theparticular second control valve 33 shown in the drawings prevents fluidflow in both directions through the valve 33.

In the embodiment of FIG. 7 preferably the second control valve 33 ismoved between its first and second positions, e.g. by the operation of asolenoid or other electrically operated actuator, under the control of amanually actuated switch, although preferably under the automaticcontrol of the switch 44 provided on the selector valve 40, to switchthe control valve 33 to its first position so that fluid is preventedfrom passing to the low pressure region 35, whenever it is desired tolower the loader arm. Desirably in this embodiment, the second controlvalve 33 is “at rest” in its second position when fluid flow through thecontrol valve 33 is permitted and an electrical signal is supplied tothe control valve 33 to move the control valve to its first position toprevent fluid flow at least to the low pressure region 35, when theselector valve 40 is operated such as to lower the loader arm.

In each of the embodiments described, by virtue of either the one waycheck valve within the first control valve 32 (in the embodiments shownin FIGS. 1 to 6) or the direct connection between the accumulator 30 andthe line 38 between the hose burst protection or check valve assembly 39and the first chamber 25 of the ram assembly 20, the pressure in theaccumulator 30 can never exceed the pressure in first chamber 25. Whenthe first control valve 32 where provided, is in its second position asseen in FIGS. 4 and 5, or permanently in the FIG. 7 embodiment, theaccumulator 30 will provide at least some ride improvement as the loadervehicle travels over the ground irrespective of the position of thesecond control valve 33, as movements of the loader arm at leastdownwardly will be damped by the action of the accumulator 30. In eachembodiment, when the second chamber 26 of the ram 20 is connected to thelow pressure region 35, when the second control valve 33 is in itssecond position, the ride improvement system will be fully active.

In each mode of operation described above, in the event of a host burstin the line 38 b between the host burst protection of check valveassembly 39 and the selection valve 40 when highly pressurised, e.g.during lifting, or in the hose between where the second control valve 33and the line 42 to the selection valve 40 are connected when highlypressurised, e.g. during lowering, the hose burst protection or checkvalve assembly 39 will be closed or close, to prevent the escape ofpressurised fluid from the line 38 a between the first chamber 25 andthe hose burst protection or check valve assembly 39, so that the loaderarm is prevented from collapsing and thus possible creating an unstableand possibly dangerous situation.

Although the invention has been described in relation to a wheeledloader vehicle, it will be appreciated that the invention may be appliedto any other mobile machine requiring a ride improvement system for aloader arm. For example the invention may be applied to a tracked orpartly tacked machine or vehicle, or to a mobile crane.

The features disclosed in the foregoing description, or the followingclaims, or the accompanying drawings, expressed in their specific formsor in terms of a means for performing the disclosed function, or amethod or process for attaining the disclosed result, as appropriate,may, separately, or in any combination of such features, be utilised forrealising the invention in diverse forms thereof.

1-6. (canceled)
 7. A hydraulic system for a wheeled loader having aloader arm assembly which is movable between raised and loweredpositions by means of a hydraulic actuator device, the systemcomprising: a selection valve having first and second ports fordirecting hydraulic fluid to a cylinder, the cylinder having first andsecond chambers, the first chamber connected to the first port and thesecond chamber connected to the second port; a hydraulic accumulatorconnected to the hydraulic actuator device between the first port andthe first chamber; a first control valve connected to the hydraulicactuator device between the hydraulic accumulator and the first chamber;a second control valve connected to the hydraulic actuator devicebetween the second port and the second chamber, the second control valvefurther connected to a hydraulic reservoir; and a hose burst check valveconnected to the hydraulic actuator device between the first port andthe hydraulic accumulator; wherein the first control valve is movablebetween a first position in which passage of hydraulic fluid ispermitted only from the hydraulic accumulator toward the first chamberand a second position in which passage of hydraulic fluid is permittedin bi-directionally between the hydraulic accumulator and the firstchamber, the second control valve is movable between a first position inwhich passage of hydraulic fluid through the second control valve isprevented and a second position in which passage of hydraulic fluidthrough the second control valve is permitted, and the hose burst checkvalve normally allows one-way hydraulic fluid flow from the first portto the first chamber, but the hose burst check valve is arranged topermit two-way hydraulic fluid flow between the first chamber and thefirst port when hydraulic fluid is directed from the second port to thehose burst check valve.
 8. The system according to claim 7 wherein thehose burst check valve is a pilot valve.
 9. The system according toclaim 7 wherein the selection valve is manually operable.
 10. The systemaccording to claim 7 wherein the first and second control valves areelectrically operated solenoid valves to which current is supplied by amanually operable switch means.
 11. The system according to claim 7wherein the first and second control valves are biased towards the firstposition.
 12. The system according to claim 11 wherein the first andsecond control valves are spring biased towards the first position. 13.The system according to claim 7 wherein at least one of saidaccumulator, control valves, check valve assembly and connecting pipesare made of metal.